Free piston engine



Original Filed March 9, 1961 INVENTOR Hare/o Kosqff ATTORNEY United States Patent 3 Claims. (or. 123- 16 This case is a division of my application Serial No. 105,527 entitled Free Piston Engine filed on March 9, 1961 now abandoned.

This invention relates to an improvement in the free piston engine wherein mechanical devices hitherto required for synchronization of opposed pistons are eliminated.

The free piston engine in its most basic form may be defined as a piston-cylinder device in which combustion products in a combustion chamber urge the piston to compress an enclosed volume, which in turn provide the energy to compress the combustion chamber in preparation for the next combustion. The difference in energy reqiured to compress the fluid in the combustion chamber and the energy released by expansion of the combustion products is available for useful work.

Commonly used mechanical devices for synchronizing opposed pistons of a free-piston engine cause friction and fluid losses, add to the size and weight, increase the complexity, and decrease the reliability of the engine.

An object of this invention is to provide a free piston engine in which synchronization of opposed pistons is achieved by a novel arrangement of functionally interrelated conduits by which the physical variables of the system are both self-sensing and self-controlling.

A further object of this invention is to increase the engine flexibility by allowing the arrangement of an arbitrary number of piston-cylinder combinations around a common chamber without the encumbrance of complex mechanical linkage.

The nature of this invention is such that the theory and the several illustrated means of implementation of this theory are applicable to the entire class of internal combustion engines having one or more elastic volumes, and having pistons which are maintained in reciprocating motion by elastic forces.

The sole figure is a sectional view of a free piston engine including a pneumatic embodiment of this inven- 5 control any two variables of an operative engine.

tion and means for limiting the most inward piston position. This view shows the pistons at the nominal outer limit of motion.

A system by which the compression ratio and outer limit of piston motion may be maintained constant in an engine having no mechanical linkage is described at length in my co-pending application, Serial Number 76,933 filed December 19, 1960 and now Patent No. 3,127,881.

In application 76,933 the invention claimed therein is explained by using the following theorems from me chanics:

(I) The center of mass of a system moves as if the total external force were acting on the entire mass of the system concentrated at the center of mass.

(II) If a mass is bound by elastic material and the kinetic energy over a finite period of time is not zero, the mass in fact will be oscillating.

Since the present invention also rests on the same phys ical principles, the theory presented in Ser. No. 76,933 will not be repeated herein. In accordance with the present invention I provide means for sensing the piston position toward the end of its out-stroke and applying a fluid pressure axially to said piston to control its average position.

In a two piston free piston engine the two rebounce $357,155 Patented Nov. 17., 1964 chambers allow two degrees of freedom and each piston has associated with it two frequencies of oscillation: the piston oscillation and the oscillation of the center of mass of the system. The two degrees of freedom may Any chamber defined in part by the piston including the rebounce chamber may be the means for applying a variable force axially on the piston. From a practical point of view, it is most desirable to control the compression ratio and the average position of the center of mass by means of a variable force in the rebounce chamber.

Refer to the sole figure. The free piston engine shown includes a combustion chamber 1, two pump chambers 2, two rebounce chambers 3, two pistons 4, intake port 5, exhaust port 6, and a fuel meter/injector 7. The injector 7 is not part of this invention. It may be any conventional one and is depicted herein solely as part of an illustrative environment for the present invention. A conduit 41 is connected to an aperture 40 in the cylinder walls. Changes in the pressure in the combustion chamber actuate the injector '7. Conduit 25 connects the fuel meter/injector with a fuel supply (not shown). At the time of combustion, the combustion chamber 1 pressure causes the pistons 4 to move toward their most outward positions. Energy stored in the compressed air (or other compressible fiuid) in the rebounce chambers 3 restores the pistons to their most inward positions and provides the energy for pumping the fluid within the pump chamber.

It is necessary for synchronized piston motion that piston position sensing means be provided which are functionally connected to means for producing adjustable forces acting on the pistons. By varying these forces the deviation of the systems center of mass from the engines center may be reduced to a small value. If the sensing devices sense a shift in the systems center of mass to the left of the engines center, the net force acting on the pistons is increased toward theright by the adjustable forces. Conversely, if the sensing devices sense a shift in the center of mass position to the right of center, the net force acting on the pistons is increased toward the left by the adjustable forces. In the preceding manner, the time average deviation of the center of mass position from engine center will approach zero.

In the free piston engine shown in the sole figure, the above principles are implemented by the piston-position sensing device 8 which are vents in the wall of the cylinder.

Small orifice 359 communicates an accumulator 31 with a fluid source 14 via conduit 15. Conduits l3 communicate vents 8 with the accumulator. Vents 8 are positioned near the desired maximum out-stroke of the inner faces of the wide diameter positions of the pistons 4. Grooves 32 circumscribe the pistons and communicate with their respective rebounce chambers 3 via passageways 33. The grooves and vents are so positioned that communication occurs between the rebounce chambers 3 and accumulator 31 near the end of the outward stroke and the start of the inward stroke.

In operation the pressure in the accumulator is continuously increased by the flow of pressurized fluid from source 14 via the orifice 30. Near the maximum outstroke of the piston, the grooves 32 and vents 8 are in juxtaposition. If the center of mass of the system shifts to the left of the engine center, the left groove and vent will coincide before the right groove and vent coincide. Thus, the flow of fluid from the accumulator 31 will be directed primarily into the left rebounce chamber causing a pressure (increase in this chamber greater than that in the right rebounce chamber. The net force acting on the pistons is thereby increased toice u: ward the right, i.e., in a direction which lessens the deviation of the center of mass from the center. Conversely, for a shift to the right of center, the net force acting on the pistons is increased toward the left, i.e., in a direction which lessens the deviation.

Since the preceding action occurs near the end of the outward stroke, the coincidence of the grooves and vents immediately following at the beginning of the compression stroke will occur before any appreciable pressure rise in the accumulator. On the other hand, the relatively large time interval between coincidence of the grooves and vents at the beginning of the compression stroke and their coincidence at the end of the following combustion stroke is sufiicient for the pressure in the accumulator to be restored, via orifice 30 to a relatively high value. Natural leakage of the compressed fluid from the rebounce chamber past the larger diameter positions of the pistons or leakage through apertures included for that purpose may be used to complete the pneumatic circuit. In this illustration, vents 34 enable the rebounce chamber to communicate with a fluid receiver (i.e., the atmosphere) at the end of the compression stroke and start of the combustion stroke.

During the engine operation each rebounce chamber will undergo a fluid loss and a pressure decrease continuously via leakage and/or intermittently via a vent. It will also gain fluid and increase in pressure intermittently in proportion to the deviation of the center of mass position from center. At steady state conditions the net flow of pressurized fluid through each rebounce chamber will approach zero, i.e., the loss by leakage or vent (34) exposure is equal to the intermittent fluid gain via the vents 8. Since the average losses in each rebounce chamber approach equality during steady state operation, the intermittent fluid gain in each rebounce chamber Will also approach equality. This means that each of the vents 8 has equal time-average exposure to one of the grooves 32. This also means that the average position of the pistons is neither to the right or left but rather is approximately at the center of the engine. Since the average piston position is approximately at the engine center, the pistons are synchronized.

If the variable pressure in the chamber were to act on the piston in a direction opposite to that described, the fluid source and receiver would be interchanged.

A free piston engine having synchronizing means as defined in this application is operative under the most diverse operating conditions, and further does not suffer the disadvantage of mechanical linkage and complex servo-mechanical devices hitherto found in a free piston engine.

It is understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departing from its spirit as defined in the following claims.

I claim:

1. A free piston engine comprising:

(a) a plurality of cylinders,

(b) a corresponding plurality of pistons arranged for reciprocating axial movement in said cylinders, said pistons each having a circumferential groove and also having a passageway, communicating therewith, said passageway opening into the respective rebounce chambers formed by the outer faces of said pistons and said cylinders,

(c) at least one opening in each cylinder wall located so as to communicate with said groove approximately at the end of the outward stroke of each piston,

(d) a source of gas under pressure coupled to each opening and arranged to apply said gas to said chamher when and to the extent said piston grooves communicate with said openings, and

(e) at least one vent in each cylinder to permit escape of said pressurized gas to a fluid receiver external to said cylinders,

2. The engine according to claim 1 wherein said vents are so located as to communicate with said rebounce chamber approximately at the end of the inward strokes of said pistons.

3. A free piston engine comprising:

(a) a source of gasunder pressure,

(b) a selected number of cylinders each including (1) a selected number of vents therein which communicate with a fluid receiver external to said cylinders, and

(2) openings communicating with said source (0) a selected number of pistons arranged for axial movement within said cylinders, outer faces of said pistons and portions of said cylinders defining rebounce chambers, said pistons having passageways formed therein to provide communication between said source and said rebounce chambers via said openings substantially only when said pistons are approximately at their outermost positions whereby the pressure of said gas against said pistons is varied as a function of said outermost positions, said pistons being arranged to permit gas in said rebounce chambers to escape via said vents to said receiver when said pistons move to approximately their most inward positions.

References Cited by the Examiner UNITED STATES PATENTS 2,025,177 12/35 Pescara 230-56 2,849,995 9/59 Lewis 123-46 2,916,025 12/59 Klotsch 123-46 2,983,098 5/61 Bush 60-13 3,005,306 10/61 Bush 60-13 KARL J. ALBRECHT, Acting Primary Examiner. 

1. A FREE PISTON ENGINE COMPRISING: (A) A PLURALITY OF CYLINDERS, (B) A CORRESPONDING PLURALITY OF PISTONS ARRANGED FOR RECIPROCATING AXIAL MOVEMENT IN SAID CYLINDERS, SAID PISTONS EACH HAVING A CIRCUMFERENTIAL GROOVE AND ALSO HAVING A PASSAGEWAY, COMMUNICATING THEREWITH, SAID PASSAGEWAY OPENING INTO THE RESPECTIVE REBOUNCE CHAMBERS FORMED BY THE OUTER FACES OF SAID PISTONS AND SAID CYLINDERS, (C) AT LEAST ONE OPENING IN EACH CYLINDER WALL LOCATED SO AS TO COMMUNICATE WITH SAID GROOVE APPROXIMATELY AT THE END OF THE OUTWARD STROKE OF EACH PISTON, (D) A SOURCE OF GAS UNDER PRESSURE COUPLED TO EACH OPENING AND ARRANGED TO APPLY SAID GAS TO SAID CHAMBER WHEN AND TO THE EXTENT SAID PISTON GROOVES COMMUNICATE WITH SAID OPENINGS, AND (E) AT LEAST ONE VENT IN EACH CYLINDER TO PERMIT ESCAPE OF SAID PRESSURIZED GAS TO A FLUID RECEIVER EXTERNAL TO SAID CYLINDERS. 